Liquid crystal display units, which are built in, for example, liquid crystal display-based devices such as personal computers, television sets and cellular phones, have light diffusion films or light diffusion sheets (collectively referred to as “light diffusion films” in the present specification) installed in the backlight units thereof for the purpose of improving visibility.
The most fundamental optical characteristics required for light diffusion films include a total light transmittance of visible light of 90% or more and a haze value of 70% or more.
As light diffusion films, those having the surface roughened have been known.
Such light diffusion films have been produced by roughening the surface of transparent films of resins such as polyethylene terephthalate resin, polymethylmethacrylate resin and polycarbonate resin by embossing or sandblasting; however, it has been difficult to obtain light diffusion films excellent in both light transmission and light diffusivity by simply roughening the surface of the films.
As those that have solved the above-mentioned problems, there are light diffusion films that have light diffusing materials dispersed therein and light diffusion films that have a light diffusion layer formed on the surface thereof.
As the light diffusion films having light diffusing materials dispersed therein, those in which light diffusing materials such as calcium carbonate, titanium oxide, glass beads, silica particles, polystyrene particles, silicone resin particles and crosslinked polymer particles are dispersed in transparent resinous films are known.
However, such light diffusion films as described above are high in viscosity of the resins which form the films, and thus suffer from a problem such that it is difficult to uniformly disperse the light diffusing materials. Therefore, light diffusion films having a light diffusion layer formed on the surface thereof have come to be explored.
As the light diffusion films having a light diffusion layer formed on the surface thereof, those which are produced by coating the surface of the films with a composition of a light diffusing material dispersed in a solution of a plastic or curable resin binder, followed by drying or curing are known (for example, Patent Documents 1 to 3).
Patent Document 1: Japanese Patent Laid-Open No. H07-209502 (Claims)
Patent Document 2: Japanese Patent Laid-Open No. H07-218705 (Claims)
Patent Document 3: Japanese Patent Laid-Open No. H11-160505 (Claims)